How Do Prosthetic Arms Work?

Modern prosthetic arms have moved well beyond cables and hooks. Today’s bionic arms read muscle signals, are built from 3D-printed materials, and attach to the body without surgery or harnesses. Three questions come up consistently for anyone exploring upper limb prosthetics: how do they function, how are they attached, and what are they made of.

How Prosthetic Arms Function

Myoelectric prosthetic arms, like our Hero Arm, are controlled by the electrical signals muscles produce when they contract. Sensors called EMG electrodes inside the socket rest against the skin and detect those signals. When the user flexes to close their hand, the electrodes pick up the signal, the arm’s electronics interpret it, and motors in the hand create movement. The control is proportional: a gentle flex produces a light grip, a stronger contraction closes the hand firmly.

This works even for people born without a hand. The muscles responsible for wrist flexion and extension are usually still present in the residual limb and can produce signals.

Advanced myoelectric prosthetics like Hero PRO or Hero RGD use MyoPods, which are wireless EMG sensors that sit on the skin though cutouts in the 3D printed socket. MyoPods self-adjust their sensitivity throughout the day, are fully waterproof, and can be placed anywhere on the body. Users can also use MyoPods to customize grip sets and switch between modes using the Sidekick App.

“Now patients can see the hand respond to their own muscle signals within seconds using the wireless MyoPod sensors,” said Elise Dreiling, Director of Clinical Operations and certified prosthetist at the Open Bionics clinic in Denver. “It’s often the first time a patient realises how intuitive the controls can feel. It turns a technical fitting into a meaningful moment.”

For users who have worn body-powered devices, the shift to myoelectric control feels natural.

“From the moment you put on a Hero Arm, it begins listening,” said Lucas, a Hero Pro user. “I am not pulling cables with my body. I am simply flexing a muscle, the same way I always have.”

How Prosthetic Arms Are Attached

Prosthetic arms do not require surgery or implants. They are held in place through a custom-fitted socket that uses the shape of the residual limb for suspension.

The socket is fabricated from a 3D scan of the limb, capturing every curve and contour. A flexible inner liner made from a medically certified elastomer sits against the skin, providing a breathable interface that can be removed for cleaning. Suspension is achieved through the total contact fit and targeted pressure near prominent areas of the arm, without pins, locks, or harnesses.

The Hero Arm, Hero PRO, and Hero RGD all feature a BOA fit dial, which allows the user to adjust socket tension throughout the day with a single turn. The arm can be put on and taken off at will.

“Sliding the socket onto my arm for the first time felt natural,” Lucas said. “Snug but gentle. I could lift, grip, and move without thinking about the attachment. The arm is a choice. I can put it on or take it off at will. That freedom makes all the difference.”

What Prosthetic Arms Are Made Of

Traditional prosthetic arms are built from aluminum, steel, and hard plastics. These materials are durable but add weight and can feel rigid over a full day of wear.

Our prosthetic arms are built from Nylon PA12, a high-performance material used in industrial 3D printing. PA12 is strong enough to house motors, wiring, and joints while remaining significantly lighter than metal alternatives. The inner socket is printed in a flexible material with a vented design to allow airflow and reduce heat during extended wear. The Hero PRO integrates its battery directly into the hand to keep weight balanced and achieve IPX7 water resistance. The Hero RGD adds titanium joints and a shock-absorbing palm, rated to IPX8, carrying up to 77 pounds and closing its fingers in less than half a second. The bionic hand can be swapped out for Activity Attachments thanks to our USMC-standard titanium wrist, which is rated to more than 220 pounds, allowing the same socket to support work tools, sport grips, or a bionic hand interchangeably.

Because everything starts from a 3D scan, every dimension of the socket and frame can be adjusted in the digital model before a component is produced. Thickness, curvature, ventilation, and cover design are all customisable to the individual.

To see how a bionic arm fits and functions in person, book a free consultation at your nearest Open Bionics clinic.